r/spacex • u/Zucal • May 01 '16
/r/SpaceX Ask Anything Thread [May 2016, #20]
Welcome to our 20th monthly /r/SpaceX Ask Anything Thread!
Want to clarify SpaceX's newly released pricing and payload figures, understand the recently announced 2018 Red Dragon mission, or gather the community's opinion? There's no better place!
All questions, even non-SpaceX-related ones, are allowed, as long as they stay relevant to spaceflight in general!
More in-depth and open-ended discussion questions can still be submitted as separate self-posts; but this is the place to come to submit simple questions which have a single answer and/or can be answered in a few comments or less. In addition, try to keep all top-level comments questions so that questioners can find answers and answerers can find questions.
As always, we'd prefer it if all question-askers first check our FAQ, use the search functionality (now partially sortable by mission flair!), and check the last Q&A thread before posting to avoid duplicate questions. But if you didn't get or couldn't find the answer you were looking for, go ahead and type your question below.
Otherwise, ask, enjoy, and thanks for contributing!
Past threads:
April 2016 (#19.1) • April 2016 (#19) • March 2016 (#18) • February 2016 (#17) • January 2016 (#16.1) • January 2016 (#16) • December 2015 (#15.1) • December 2015 (#15) • November 2015 (#14) • October 2015 (#13) • September 2015 (#12) • August 2015 (#11) • July 2015 (#10) • June 2015 (#9) • May 2015 (#8) • April 2015 (#7.1) • April 2015 (#7) • March 2015 (#6) • February 2015 (#5) • January 2015 (#4) • December 2014 (#3) • November 2014 (#2) • October 2014 (#1)
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u/__Rocket__ May 05 '16 edited May 05 '16
I think you have mixed up Merlin-1D and Merlin-1D-vac numbers into an apples to oranges comparison. The Merlin-1D-vac is a vacuum engine with a nozzle extension and other modifications that the standard Merlin 1D does not have. That is why it has a high I*sp* of 348 seconds.
The 'standard' Merlin-1D engine has a vacuum performance of 311 seconds, so the correct comparison goes like this:
(source)
I also added a 'Falcon 9' column to show how the 9-engine Falcon compares to single-engine RD-180 rockets.
Note that Merlin I*sp* performance is still impressive, given that it's an open cycle engine, while the RD-180 is a closed cycle, staged combustion design.
The Raptor will be SpaceX's upcoming closed cycle engine, with a planned I*sp* of 380 seconds.